Were there really a 64 production or are they really 65's

The very first Mustangs were sold as a "!964 1/2" model, and the easiest way to identify them is through the heater controls: they all had a 2-speed fan, the '65 started using the 3-speed unit. '65s had an alternator as where the earlier ones had generators, but it's tough to go by that as they may have been upgraded later. The "fastback" or 2+2 came out later in 1965- there are no 1964 1/2 fastbacks.

From Wikipedia: The Ford Mustang was brought out five months before the normal start of the 1965 production year. The earliest versions are often referred to as 1964½ models, but VIN coded by Ford and titled as 1965 models, though minor design updates for fall 1965 contribute to tracking 1964½ production data separately from 1965 data (see data below).[9] with production beginning in Dearborn, Michigan on March 9, 1964;[10] the new car was introduced to the public on April 17, 1964[11] at the New York World's Fair.[12] --- http://en.wikipedia.org/wiki/Ford_Mustang

Another way to identify the difference between 1965 models and post-July 1964 models is the headlamp bezel: How to Identify a '64-1/2 Mustang - http://www.mustangandfords.com/news/mustang-1964/